Listen to Robert Emmerich introduce "The Big Apple," a hit song from 1937. Music written by Bob and performed by Tommy Dorsey's Clambake Seven with Bob on piano. Lyrics written by Buddy Bernier and sung by Edythe Wright. Audio provided by Dorothy Emmerich.

"It’s immoral to let a sucker keep his money” (or, “It’s morally wrong to let a sucker keep his money") has been attributed to “Canada Bill” Jones (?-1880) in 1978, P. T. Barnum (1810-1891) in 1979, and W. C. Fields (1880-1946) in 2002. The gambling saying means that a professional sharp is obligated to take a sucker’s (amateur’s) money.

Wikipedia: Canada Bill JonesWilliam “Canada Bill” Jones (?-1880) was a noted confidence artist, riverboat gambler and card sharp. He has been described as “without doubt the greatest three-card-monte sharp ever to work the boats, perhaps the greatest of them all.”
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Quotations
“It’s immoral to let a sucker keep his money”

25 June 1982, Los Angeles (CA) Times, “Morning Briefing,” pg. SD B2:
Add Sleinbrenner: After being introduced as a man who “operates under the P. T. Barnum principle that says it is morally wrong to allow a sucker to keep any of his money,” Steinbrenner said, “Ownership of ports franchises is a big ego trip, and don’t let anybody tell you any differently.”

Google Books500 of the Most Witty, Acerbic & Erudite Things Ever Said About Money
By Philip Jenks
Petersfield, Hampshire: Harriman House Ltd.
2002
Pg. 34:
‘It is morally wrong to allow a sucker to keep his money.’
W. C Fields

The Herald (Scotland)
Monday 18 June 2007
The different brand of bung that exists in Spain . . . or does it?
Mark Wilson on Monday
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As WC Fields once put it, it’s morally wrong to allow a sucker to keep his money.